Aluminum-zirconium-titanium-carbon grain refiner for magnesium and magnesium alloys and method for producing the same

ABSTRACT

The present invention pertains to the field of metal alloy, and discloses an aluminum-zirconium-titanium-carbon grain refiner for magnesium and magnesium alloys, having a chemical composition of: 0.01%˜10% Zr, 0.01%˜10% Ti, 0.01%˜0.3% C, and Al in balance, based on weight percentage. Also, the present invention discloses the method for preparing the grain refiner. The grain refiner according to the present invention is an Al—Zr—Ti—C intermediate alloy having great nucleation ability and in turn excellent grain refining performance for magnesium and magnesium alloys, and is industrially applicable in the casting and rolling of magnesium and magnesium alloy profiles, enabling the wide use of magnesium in industries.

FIELD OF THE INVENTION

The present invention relates to an intermediate alloy for improving theperformance of metals and alloys by refining grains, and, especially, toa grain refiner for magnesium and magnesium alloy and the method forproducing the same.

BACKGROUND OF THE INVENTION

The use of magnesium and magnesium alloy in industries started in 1930s.Since magnesium and magnesium alloys are the lightest structuralmetallic materials at present, and have the advantages of low density,high specific strength and stiffness, good damping shock absorption,heat conductivity, and electromagnetic shielding performance, excellentmachinability, stable part size, easy recovery, and the like, magnesiumand magnesium alloys, especially wrought magnesium alloys, possessextremely enormous utilization potential in the filed of transportation,engineering structural materials, and electronics. Wrought magnesiumalloy refers to the magnesium alloy formed by plastic molding methodssuch as extruding, rolling, forging, and the like. However, due to theconstraints in, for example, material preparation, processingtechniques, anti-corrosion performance and cost, the use of magnesiumalloy, especially wrought magnesium alloy, is far behind steel andaluminum alloys in terms of utilization amount, resulting in atremendous difference between the developing potential and practicalapplication thereof, which never occurs in any other metal materials.

The difference of magnesium from other commonly used metals such asiron, copper, and aluminum lies in that, its alloy exhibitsclosed-packed hexagonal crystal structure, has only 3 independent slipsystems at room temperature, is poor in plastic wrought, and issignificantly affected by grain sizes in terms of mechanical property.Magnesium alloy has relatively wide range of crystallizationtemperature, relatively low heat conductivity, relatively large volumecontraction, serious tendency to grain growth coarsening, and defects ofgenerating shrinkage porosity, heat cracking, and the like duringsetting. Since finer grain size facilitates reducing shrinkage porosity,decreasing the size of the second phase, and reducing defects inforging, the refining of magnesium alloy grains can shorten thediffusion distance required by the solid solution of short grainboundary phases, and in turn improves the efficiency of heat treatment.Additionally, finer grain size contributes to improving theanti-corrosion performance and machinability of the magnesium alloys.The application of grain refiner in refining magnesium alloy melts is animportant means for improving the comprehensive performances and formingproperties of magnesium alloys. The refining of grain size can not onlyimprove the strength of magnesium alloys, but also the plasticity andtoughness thereof, thereby enabling large-scale plastic processing andlow-cost industrialization of magnesium alloy materials.

It was found in 1937 that the element that has significantly refiningeffect for pure magnesium grain size is Zr. Studies have shown that Zrcan effectively inhibits the growth of magnesium alloy grains, so as torefine the grain size. Zr can be used in pure Mg, Mg—Zn-based alloys,and Mg-RE-based alloys, but can not be used in Mg—Al-based alloys andMg—Mn-based alloys, since it has a very small solubility in liquidmagnesium, that is, only 0.6 wt % Zr dissolved in liquid magnesiumduring peritectic reaction, and will be precipitated by forming stablecompounds with Al and Mn. Mg—Al-based alloys are the most popular,commercially available magnesium alloys, but have the disadvantages ofrelatively coarse cast grains, and even coarse columnar crystals andfan-shaped crystals, resulting in difficulties in wrought processing ofingots, tendency to cracking, low finished product rate, poor mechanicalproperty, and very low plastic wrought rate, which adversely affects theindustrial production thereof. Therefore, the problem existed inrefining magnesium alloy cast grains should be firstly addressed inorder to achieve large-scale production. The methods for refining thegrains of Mg—Al-based alloys mainly comprise overheating method, rareearth element addition method, and carbon inoculation method. Theoverheating method is effective to some extent; however, the melt isseriously oxidized. The rare earth element addition method has neitherstable nor ideal effect. The carbon inoculation method has theadvantages of broad source of raw materials and low operatingtemperature, and has become the main grain refining method forMg—Al-based alloys. Conventional carbon inoculation methods add MgCO₃,C₂Cl₆, or the like to a melt to form large amount of disperse Al₄C₃ masspoints therein, which are good heterogeneous crystal nucleus forrefining the grain size of magnesium alloys. However, such refiners areseldom adopted because their addition often causes the melt to beboiled. In summary, in contrast with the industry of aluminum alloys, ageneral-purpose grain intermediate alloy has not been found in theindustry of magnesium alloy, and the applicable range of various grainrefining methods depends on the alloys or the components thereof.Therefore, one of the keys to achieve the industrialization of magnesiumalloys is to find a general-purpose grain refiner capable of effectivelyrefining cast grains when solidifying magnesium and magnesium alloys.

SUMMARY OF THE INVENTION

For the purpose of addressing the disadvantages existing in the aboveprior art, the present invention provides analuminum-zirconium-titanium-carbon intermediate alloy for refining thegrains of magnesium and magnesium alloys, which has great nucleationability for magnesium and magnesium alloys. Also, the present inventionprovides a method for producing the intermediate alloy.

Surprisingly, the present inventor found that both Al₄C₃ and ZrC possessnucleation ability, and ZrC is a crystal nucleus having nucleationability as many times as that of the Al₄C₃ in large number of studies onthe refining of magnesium alloy grains. However, both Al₄C₃ and ZrC arenot easy to be obtained. The present inventor readily prepared anAl—Zr—Ti—C intermediate alloy, in which large amount of mAl₄C₃.nZrC.pTiCparticle agglomerate were observed in the gold phase via scanningelectromicroscopic diagram and energy spectrum analysis. The obtainedAl—Zr—Ti—C intermediate alloy has relatively low melting point, so thatit can form large amount of disperse ZrC and Al₄C₃ mass points, actingas the best non-homogeneous crystal nucleus for magnesium alloys.

The present invention adopts the following technical solutions: Analuminum-zirconium-titanium-carbon grain refiner for magnesium andmagnesium alloys has a chemical composition of: 0.01%˜10% Zr, 0.01%˜10%Ti, 0.01%˜0.3% C, and Al in balance, based on weight percentage.

Preferably, the aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C)intermediate alloy has a chemical composition of: 0.1%˜10% Zr, 0.1%˜10%Ti, 0.01%˜0.3% C, and Al in balance, based on weight percentage. Themore preferable chemical composition is: 1%˜5% Zr, 1%˜5% Ti, 0.1%˜0.3%C, and Al in balance.

Preferably, the contents of impurities present in thealuminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy are:Fe≦0.5%, Si≦0.3%, Cu≦0.2%, Cr≦0.2%, and other single impurityelement≦0.2%, based on weight percentage.

A method for producing an aluminum-zirconium-titanium-carbon grainrefiner for magnesium and magnesium alloys according to the presentinvention comprises the steps of:

-   -   a. preparing the above raw materials according to their weight        percentage, melting commercially pure aluminum, heating to a        temperature of 1000° C.-1300° C., and adding zirconium scarp,        titanium scarp and graphite powder thereto to be dissolved        therein, and    -   b. keeping the temperature under agitation for 15-120 minutes,        and performing casting molding.

The present invention achieves the following technical effects: anAl—Zr—Ti—C intermediate alloy which has great nucleation ability and inturn excellent ability in refining the grains of magnesium and magnesiumalloys is invented, in which large amount of mAl₄C₃.nZrC.pTiC particleagglomerate are present, wherein m:n:p is about(0.61˜0.75):(0.1˜0.2):(0.1˜0.2). The obtained intermediate alloy canform large amount of disperse ZrC and Al₄C₃ mass points acting asnucleus, greatly facilitating the grain refining of magnesium ormagnesium alloy microstructure. It has good wrought processingperformance, and can be easily rolled into a wire material of Φ9˜10 mmfor industrial production. As a grain refiner, the intermediate alloy isindustrially applicable in the casting and rolling of magnesium andmagnesium alloy profiles, enabling the wide use of magnesium inindustries.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is the SEM calibration graph of Al—Zr—Ti—C intermediate alloysmagnified by 3000;

FIG. 2 is the energy spectrum of point A in FIG. 1;

FIG. 3 is the grain microstructure of pure magnesium; and

FIG. 4 is the grain microstructure of pure magnesium subjected to grainrefining by the Al—Zr—Ti—C intermediate alloy.

DETAILED DESCRIPTION

The present invention can be further clearly understood in combinationwith the particular examples given below, which, however, are notintended to limit the scope of the present invention.

EXAMPLE 1

948.5 kg commercially pure aluminum (Al), 30 kg zirconium (Zr) scarp, 20kg titanium (Ti) scarpand 1.5 kg graphite powder were weighed. Thealuminum was added to an induction furnace, melt therein, and heated toa temperature of 1050° C.±10° C., in which the zirconium scarp, thetitanium scarp and the graphite powder were then added and dissolved.The resultant mixture was kept at the temperature under mechanicalagitation for 100 minutes, and directly cast into Waffle ingots, i.e.,aluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy. FIG.1 shows the SEM photographs of Al—Zr—Ti—C intermediate alloy at 3000magnification, in which the gray blocks are larger particles, having aparticle size of 20 μm-100 μm; and the polygonal thin sheets are smallerparticles, having a particle size of 1˜10 μm.

FIG. 2 is an energy spectrum of A area in FIG. 1. The standard samplesused in the test were Al:Al₂O₃; Zr:Zr; Ti:Ti; C:CaCO₃, and Zr:Zr, andthe atom percentages were 51.56% C, 37.45% Al, 7.52% Zr and 3.47% Ti,respectively.

EXAMPLE 2

942.3 kg commercially pure aluminum (Al), 45 kg zirconium (Zr) scarp, 10kg titanium (Ti) scarp and 2.7 kg graphite powder were weighed. Thealuminum was added to an induction furnace, melt therein, and heated toa temperature of 1200° C.±10° C., in which the zirconium scarp, thetitanium scarp and the graphite powder were then added and dissolved.The resultant mixture was kept at the temperature under mechanicalagitation for 30 minutes, and directly cast into Waffle ingots, i.e., analuminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy.

EXAMPLE 3

978 kg commercially pure aluminum (Al), 10 kg zirconium (Zr) scarp, 11kg titanium (Ti) scarp, and 1kg graphite powder were weighed. Thealuminum was added to an induction furnace, melt therein, and heated toa temperature of 1100° C.±10° C., in which the zirconium scarp, thetitanium scarp and the graphite powder were then added and dissolved.The resultant mixture was kept at the temperature under mechanicalagitation for 45 minutes, and directly cast into Waffle ingots, i.e., analuminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy.

EXAMPLE 4

972.6 kg commercially pure aluminum (Al), 25 kg zirconium (Zr) scarp,1.4 kg titanium (Ti) scarp, and 1kg graphite powder were weighed. Thealuminum was added to an induction furnace, melt therein, and heated toa temperature of 1300° C.±10° C., in which the zirconium scarp, thetitanium scarp and the graphite powder were then added and dissolved.The resultant mixture was kept at the temperature under mechanicalagitation for 25 minutes, and directly cast into Waffle ingots, i.e., analuminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy.

EXAMPLE 5

817 kg commercially pure aluminum (Al), 97 kg zirconium (Zr) scarp, 83kg titanium (Ti) scarp, and 3 kg graphite powder were weighed. Thealuminum was added to an induction furnace, melt therein, and heated toa temperature of 1270° C.±10° C., in which the zirconium scarp, thetitanium scarp and the graphite powder were then added and dissolved.The resultant mixture was kept at the temperature under mechanicalagitation for 80 minutes, and directly cast into Waffle ingots, i.e., analuminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloy.

EXAMPLE 6

997.5 kg commercially pure aluminum (Al), 1 kg zirconium (Zr) scarp, 1.2kg titanium (Ti) scarp, and 0.3 kg graphite powder were weighed. Thealuminum was added to an induction furnace, melt therein, and heated toa temperature of 1270° C.±10° C., in which the zirconium scarp, thetitanium scarp and the graphite powder were then added and dissolved.The resultant mixture was kept at the temperature under mechanicalagitation for 120 minutes, and cast and rolled into coiled wires ofaluminum-zirconium-titanium-carbon (Al—Zr—Ti—C) intermediate alloyhaving a diameter of 9.5 mm.

EXAMPLE 7

Pure magnesium was melt in an induction furnace under the protection ofa mixture gas of SF₆ and CO₂, and heated to a temperature of 710° C., towhich 1% Al—Zr—Ti—C intermediate alloy prepared according to examples1-6 were respectively added to perform grain refining. The resultantmixture was kept at the temperature under mechanical agitation for 30minutes, and directly cast into ingots to provide 6 groups of magnesiumalloy sample subjected to grain refining.

The grain size of the samples were evaluated under GB/T 6394-2002 forthe circular range defined by a radius of ½ to ¾ from the center of thesamples. Two fields of view were defined in each of the four quadrantsover the circular range, that is, 8 in total, and the grain size wascalculated by cut-off point method.

Referring to FIG. 3, it shows the grain microstructure of pure magnesiumwithout grain refining. The pure magnesium without grain refiningexhibited columnar grains having a width of 300 μmm˜2000 μm and inscattering state. FIG. 4 shows the grain microstructure of puremagnesium subjected to grain refining. The 6 groups of magnesium alloyssubjected to grain refining exhibited equiaxed grains with a width of 50μm˜200 μm.

The results of the tests show that the Al—Zr—Ti—C intermediate alloysaccording to the present invention have very good effect in refining thegrains of pure magnesium.

The Al—Zr—Ti—C intermediate alloy has great nucleation ability and inturn excellent ability in refining the grains of magnesium and magnesiumalloys. It has good wrought processing performance, and can be easilyrolled into a wire material of Φ9˜10 mm for industrial production. As agrain refiner, the intermediate alloy is industrially applicable in thecasting and rolling of magnesium and magnesium alloy profiles.

1. An aluminum-zirconium-titanium-carbon grain refiner for magnesium andmagnesium alloys, characterized in that thealuminum-zirconium-titanium-carbon grain refiner has a chemicalcomposition of: 0.01%˜10% Zr, 0.01%˜10% Ti, 0.01%˜0.3% C, and Al inbalance, based on weight percentage.
 2. Thealuminum-zirconium-titanium-carbon grain refiner for magnesium andmagnesium alloys according to claim 1, wherein thealuminum-zirconium-titanium-carbon grain refiner has a chemicalcomposition of: 0.1%˜10% Zr, 0.1%˜10% Ti, 0.01˜0.3% C, and Al inbalance, based on weight percentage.
 3. Thealuminum-zirconium-titanium-carbon grain refiner for magnesium andmagnesium alloys according to claim 2, wherein thealuminum-zirconium-titanium-carbon grain refiner has a chemicalcomposition of: 1%˜5% Zr, 1%˜5% Ti, 0.1%˜0.3% C, and Al in balance,based on weight percentage.
 4. The aluminum-zirconium-titanium-carbongrain refiner for magnesium and magnesium alloys according to claim 1,2, or 3, wherein the contents of impurities present in thealuminum-zirconium-titanium carbon grain refiner are: Fe≦0.5%, Si≦0.3%,Cu≦0.2%, Cr≦0.2%, and other single impurity element≦0.2%, based onweight percentage.
 5. A method for producing the grain refiner formagnesium and magnesium alloys according to any of claim 1, comprisingthe steps of: a. melting commercially pure aluminum, heating to atemperature of 1000-1300° C., and adding zirconium scarp, titanium scarpand graphite powder thereto to be dissolved therein, and b. keeping thetemperature under agitation for 15-20 minutes, and performing castingmolding.
 6. The aluminum-zirconium-titanium-carbon grain refiner formagnesium and magnesium alloys according to claim 2, wherein thecontents of impurities present in the aluminum-zirconium-titanium carbongrain refiner are: Fe≦0.5%, Si≦0.3%, Cu≦0.2%, Cr≦0.2%, and other singleimpurity element≦0.2%, based on weight percentage.
 7. Thealuminum-zirconium-titanium-carbon grain refiner for magnesium andmagnesium alloys according to claim 3, wherein the contents ofimpurities present in the aluminum-zirconium-titanium carbon grainrefiner are: Fe≦0.5%, Si≦0.3%, Cu≦0.2%, Cr≦0.2%, and other singleimpurity element≦0.2%, based on weight percentage.
 8. A method forproducing the grain refiner for magnesium and magnesium alloys accordingto any of claim 2, comprising the steps of: a. melting commercially purealuminum, heating to a temperature of 1000-1300° C., and addingzirconium scarp, titanium scarp and graphite powder thereto to bedissolved therein, and b. keeping the temperature under agitation for15-20 minutes, and performing casting molding.
 9. A method for producingthe grain refiner for magnesium and magnesium alloys according to any ofclaim 3, comprising the steps of: a. melting commercially pure aluminum,heating to a temperature of 1000-1300° C., and adding zirconium scarp,titanium scarp and graphite powder thereto to be dissolved therein, andb. keeping the temperature under agitation for 15-20 minutes, andperforming casting molding.
 10. A method for producing the grain refinerfor magnesium and magnesium alloys according to any of claim 4,comprising the steps of: a. melting commercially pure aluminum, heatingto a temperature of 1000-1300° C., and adding zirconium scarp, titaniumscarp and graphite powder thereto to be dissolved therein, and b.keeping the temperature under agitation for 15-20 minutes, andperforming casting molding.
 11. A method for producing the grain refinerfor magnesium and magnesium alloys according to any of claim 6,comprising the steps of: a. melting commercially pure aluminum, heatingto a temperature of 1000-1300° C., and adding zirconium scarp, titaniumscarp and graphite powder thereto to be dissolved therein, and b.keeping the temperature under agitation for 15-20 minutes, andperforming casting molding.
 12. A method for producing the grain refinerfor magnesium and magnesium alloys according to any of claim 7,comprising the steps of: a. melting commercially pure aluminum, heatingto a temperature of 1000-1300° C., and adding zirconium scarp, titaniumscarp and graphite powder thereto to be dissolved therein, and b.keeping the temperature under agitation for 15-20 minutes, andperforming casting molding.